A Review of Dynamic Tree Behaviors: Measurement Methods on Tree Sway, Tree Tilt, and Root–Plate Movement

Abstract

Urban forest ecosystems are being developed to provide various environmental services (e.g., the preservation of urban trees) to urban inhabitants. However, some trees are deteriorated asymptomatically without exhibiting an early sign of tree displacement, which results in a higher vulnerability under dynamic wind loads, especially during typhoon seasons, in the subtropical and tropical regions. As such, it is important to understand the tilt and sway behaviors of trees to cope up with the probability of tree failure and to improve the efficacy of tree management. Tree behaviors under wind loads have been broadly reviewed in the past literature, yet thorough discussions on the measurement methods for tree displacement and its analysis of broadleaf specimens are lacking. To understand the behavioral pattern of both broadleaf and conifer species, this paper presents a detailed review of sway behavior analysis from the perspectives of the aerial parts of the individual tree, including tree stem, canopy, and trunk, alongside a highlighted focus on the root–plate movement amid the soil-root system. The analytical approaches associated with the time-space domain and the time-frequency domain are being introduced. In addition to the review of dynamic tree behaviors, an integrated tree monitoring framework based on geographic information systems (GIS) to detect and visualize the extent of tree displacement using smart sensing technology (SST) is introduced. The monitoring system aims to establish an early warning indicator system for monitoring the displacement angles of trees over the territory of Hong Kong’s urban landscape. This pilot study highlights the importance of the monitoring system at an operational scale to be applicable in the urban areas showcasing the practical use of the Internet of Things (IoT) with an in-depth understanding of the wind-load effect toward the urban trees in the tropical and subtropical cities.

Unveiling Falling Urban Trees before and during Typhoon Higos (2020): Empirical Case Study of Potential Structural Failure Using Tilt Sensor

“…When the leeward root hinge breaks, the root no longer resists uprooting. The failure of T b which triggered the Sudden Alarm was likely caused by an underdeveloped soil-root system generating sudden failure under wind load [63,64].…”

Challenges and Capabilities in Estimating Snow Mass Intercepted in Conifer Canopies With Tree Sway Monitoring

“…Monitoring changes to the natural sway frequency of a tree is a low‐cost, non‐intrusive, and underexplored approach for quantifying canopy snow mass. Tree sway can be measured with several sensors, such as accelerometers (Hassinen et al., 1998; Yang et al., 2021). Based on mechanical theory for bending (Figure 1), tree sway frequency varies with: (a) changes in mass (e.g., snow interception), and (b) changes in rigidity (Bunce et al., 2019; Mayhead, 1973; Moore & Maguire, 2004).…”

Challenges and Capabilities in Estimating Snow Mass Intercepted in Conifer Canopies with Tree Sway Monitoring

“…Monitoring changes to the natural sway frequency of a tree is a low-cost, non-intrusive, and underexplored approach for quantifying canopy snow mass. Tree sway can be measured with several sensors, such as accelerometers (Hassinen et al, 1998;Yang et al, 2021). Based on mechanical theory (Figure 1), tree sway frequency varies with: (1) changes in mass (e.g., snow interception), and (2) changes in rigidity (Bunce et al, 2019;Mayhead, 1973;Moore & Maguire, 2004).…”